GM‐CSF Promotes Neutrophil PD‐L1 Expression Through the VEGFR‐2/STAT6/ CSF2 Signaling Axis in Oral Squamous Cell Carcinoma

ABSTRACT

Oral squamous cell carcinoma (OSCC) remains a highly aggressive malignancy with limited responsiveness to anti‐PD‐1 immunotherapy. Recent neoadjuvant studies combining VEGFR‐2 inhibition (VEGFR2i) with anti‐PD‐1 (aPD‐1) have yielded markedly improved pathological responses, suggesting a VEGFR‐2‐dependent immunoregulatory mechanism. Here, we identify a PD‐L1‐expressing CD66b ⁺ neutrophil‐enriched tumor‐associated population as a critical immunosuppressive population enriched in VEGFR‐2‐high OSCC tumors and associated with increased metastatic propensity and inferior patient outcomes. Using multiplex immunohistochemistry, scRNA‐seq, and flow cytometry, we demonstrate that VEGFR‐2‐overexpressing OSCC cells drive robust GM‐CSF secretion, which in turn induces PD‐L1 upregulation in neutrophils. Mechanistically, VEGFR‐2 activation promotes STAT6 phosphorylation and nuclear translocation, enabling direct transcriptional activation of CSF2 . GM‐CSF subsequently activates STAT5 and mTOR/S6K signaling in neutrophils, thereby enhancing PD‐L1 protein synthesis. Functionally, these PD‐L1 ⁺ TANs suppress CD8 ⁺ T‐cell proliferation, augment T‐cell exhaustion, and diminish cytotoxicity. Importantly, VEGFR‐2 inhibition or GM‐CSF neutralization restored CD8 ⁺ T‐cell function and improved responsiveness to anti‐PD‐1 therapy in vivo, whereas exogenous GM‐CSF impaired VEGFR2i/aPD‐1 efficacy. Collectively, our findings reveal a previously unrecognized VEGFR‐2/STAT6/ CSF2 axis that licenses neutrophil‐mediated immune suppression in OSCC. These data provide mechanistic rationale and preclinical support for targeting the VEGFR‐2/GM‐CSF‐neutrophil axis to improve the efficacy of PD‐1 blockade in OSCC.